1. Field of the Invention
The present invention relates to a corrugated cardboard tube made of single-lined corrugated cardboard and also to a pallet using a plurality of corrugated cardboard tubes as load bearing members.
2. Description of the Prior Art
Corrugated cardboard has many features. Specifically, not only is the corrugated cardboard light-weight, but it has a high physical strength for a given weight. In addition, the corrugated cardboard has a capability of absorbing impacts and shocks. For this reason, the corrugated cardboard has long been used not only as material for various boxes, but also as material forming part or the entirety of a pallet for the support of contents thereon such as disclosed in, for example, U.S. Pat. Nos. 2,728,545, 3,683,8.22, 4,831,938, 4,792,325 and 4,867,074. Unlike multiply cardboard, the corrugated cardboard is extremely easy to be dissolved, having an excellent capability of being recycled.
FIG. 12 illustrates the prior art pallet 70 comprising upper and lower tables 71 and 72 and load bearing members or flat spacer legs 73, all of which are made of corrugated cardboard. According to the prior art, each of the upper and lower tables 71 and 72 and the flat spacer legs 73 is made up a laminar structure including a plurality of webs of double-lined corrugated cardboard 2M of a structure comprising a pair of flat liner sheets 2b with a corrugated sheet 2a sandwiched and bonded in position therebetween by the use of an adhesive material. Each flat spacer leg 73 has opposite annular end faces glued to the upper and lower tables 71 and 72 by means of a suitable adhesive material so as to receive a load, imposed by contents placed on the upper table 72, in a vertical direction A perpendicular to any one of the upper and lower tables 71 and 72.
It has been found that each flat spacer leg 73 employed in the prior art pallet fails to make a maximized utilization of physical properties and workability of the corrugated cardboard 2M, and therefore, not only is the pallet still far from exhibiting a sufficient strength, but also the productivity is low.
In other words, each of the fiat spacer legs 73 employed in the prior art pallet is of a structure wherein a plurality of generally oblong flat webs of multiply double-lined corrugated cardboard 2M are bonded face-to-face together into a flat laminar structure, having opposite end faces bonded to the upper and lower tables 71 an 72. Therefore, the spacer legs 73 have a problem in that both of the compressive strength with respect to the vertical direction A in which the load acts, and the geometric moment of inertia with respect to their cross-section are low.
Moreover, when the fiat spacer legs 73 are to be manufactured, a plurality of oblong webs of corrugated cardboard must be laminated one by one before they are bonded together, and therefore the productivity of the fiat spacer legs 73 is low.
The prior art pallet 70 has an additional problem. When the pallet 70 is in use for transportation of contents by means of, for example, a forklift truck, the fiat spacer legs 73 is often subjected to a lateral load F applied thereto when load carrier pawls 80 of the forklift truck contact the flat spacer legs 73 as they protrude into a space between the upper and lower tables 71 and 72, or when a length of rope 90 used is tied to some or all of the fiat spacer legs 73 to pull the pallet 70. At this time, since the opposite end faces of the flat spacer legs 73 where the lateral load tends to be concentrated are firmly bonded by the bonding material to the respective liner sheets 2b of the innermost webs of double-lined corrugated cardboard 2M forming the respective tables 71 and 72, a so-called interlayer separation, indicated by B in FIG. 12, in which the neighboring laminated layers in the innermost liner sheet 2b of each table 71 or 72 are separated from each other tends to occur as the liners 2b are pulled laterally by the flat spacer legs 73 by the action of the lateral load F.